1Beijing Key Laboratory of Plant Protein and Cereal Processing, College of Food Science and Nutritional Engineering, China Agricultural University, 100083, Beijing, PR China
2Food Production Engineering, National Food Institute, Technical University of Denmark, 2800, Kgs. Lyngby, Denmark
Plant proteins are increasingly explored as sustainable emulsifiers. Coconut protein mainly consists of globulin and albumin, and these individual protein fractions exhibit distinct interfacial behaviors. In this study, globulin and albumin were extracted from supercritical CO₂ (SCO₂) defatted coconut meal, and their interfacial behaviors—individually and in mixture (globulin : albumin = 2 : 1, c/c) were systematically investigated at the oil–water interface. The effects of heat treatment on interfacial film formation and properties were also evaluated, including adsorption kinetics, interfacial dilatational rheology, and interfacial shear rheology.
Compared with albumin, globulin exhibited faster diffusion (k1= 6.4 × 10-3in globulinversus3.9 × 10-3in albumin) and rearrangement ( k2 = 0.5 × 10-3in globulinversus0.3 × 10-3in albumin), indicating its greater ability to occupy and reorganize the interface. Heat treatment (90 ℃, 20 min) markedly accelerated both diffusion (k1= 41.1 × 10-3in globulinversus20.4 × 10-3in albumin) and reorganization ( k2 = 1.5 × 10-3in globulinversus1.1 × 10-3in albumin). These findings suggest that interfacial rearrangement is the rate-limiting step in film formation. The mixture exhibited diffusion (k1= 6.6 × 10-3in unheated groupversus41.3 × 10-3in heated group) and rearrangement behaviors (k2= 0.5 × 10-3in unheated groupversus1.7 × 10-3in heated group) similar to globulin, but its interfacial film under dilatational deformation displayed albumin-like characteristics with lower dilatational elasticity modulus (E′ = 13.4 mN/m vs. 20.9 mN/m in globulin), suggesting complementary roles in mixed systems. Moreover, heat enhanced the film elasticity under dilatational conditions.
Interfacial shear rheology further revealed that globulin formed an elastic interfacial network more rapidly and exhibited greater resistance to mechanical deformation (linear viscoelastic region γ₀ = 2.80% in globulinversus1.64% in albumin). The mixture retained globulin-like network formation (γ₀ = 2.25%), implying globulin’s dominance under shearing. Notably, heat accelerated network formation but reduced overall film strength (lower G’).
Overall, this study elucidates the interfacial mechanisms of coconut protein fractions, providing a foundation for selecting proteins with desired interfacial functionality and offering insights into their potential for emulsion-based applications.